No doubt these Senators all voted according to their deeply held beliefs.

But you can't help notice the pattern.

There are about 1.2 million retail employees in Australia, about one in five are members of the SDA; are retail workers, unlike the rest of the voting population, more likely to oppose marriage equality? Ditto transport workers.

A small group of powerful union officials have considerable influence over pre-selections particularly for the Senate.

Marriage equality would be much more likely to pass the Senate if the ALP had a more open pre-selection process.